Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $232.47   3.802%   $241.3085   $241.31   $241.30   $241.30  
  Purchase #2 $210.43   6.574%   $224.2637   $224.26   $224.25   $224.30  
  Purchase #3 $98.56   6.699%   $105.1625   $105.16   $105.15   $105.20  
  Purchase #4 $227.77   8.210%   $246.4699   $246.47   $246.45   $246.50  
  Purchase #5 $73.85   10.695%   $81.7483   $81.75   $81.75   $81.70  
  Purchase #6 $225.49   5.337%   $237.5244   $237.52   $237.50   $237.50  
  Purchase #7 $119.40   13.423%   $135.4271   $135.43   $135.45   $135.40  
  7 purchase totals = $1,187.97       $1,271.9044   $1,271.90   $1,271.85   $1,271.90